And what's the denotational semantics of type classes? As far as I know it has never been done, because it's very complex. On Tue, May 6, 2008 at 2:57 PM, Achim Schneider wrote:

Well, it's an unformalised and not much thought about out-of-the-tub idea, but here it goes:

Let there be a monad/typeclass representing the denotional semantics of Haskell

Do some instances of it, called e.g. GHC or Hugs.

so, instead of

main :: IO ()

we have

main :: (Haskell h) => h (IO ())

or, if you need some feature of the Haskell runtime system XYZ

main :: XYZ (IO ())

or even

main :: (FFI h) => h (IO ())

and

main :: (SomeLib h) => h (IO ())

, and then go on and define every single language construct as part of this type hierarchy, and define some syntactic sugar to make stuff look exactly like haskell '98 if you're just hacking away.

I especially like the metacircularity of this approach, and the fact that every Model (read: implementation) of Haskell would have to admit that it is only a Model (read: instance) of Haskell.

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